This invention relates to an attachment for a percussive rock drilling machine of the kind being displaceable along a feed beam by a feeding device, said attachment being arranged for during applied rearward feed force withdraw drill steels which are stuck in the drilled hole.
A frequently appearing problem in rock drilling is that the drill steel or the drill string gets stuck in the drilled hole, for example due to loose material falling from the sides of the hole and wedging the drill bit. Quite often the withdrawing power of the feeding device is unsufficient to loosen the drill steel, and the steel is usually left in the hole. Withdrawing the drill steel by jacks applied between the drill steel and the rock surface is mostly not successful since the drill steel or the drill bit or both of them get damaged by the lifting action. A better result is achieved by using specially made percussive machines which are coupled on to the drilling rig in use. Machines of that kind comprise an impact motor adapted to force out the drill steel from the drill hole by impacts, i.e. in principal a percussive drilling machine striking upwards instead of downwards. Such machines are, however, too expensive to have in store only for this exceptional use and are difficult to couple on to the feed beam and power system of the equipment in use.
One object of the present invention is therefore to provide a simple and economical attachment for withdrawing stuck drill steels, which attachment easily can be coupled on to the drilling machine in use when the drill steel is stuck. Another object is to make it possible to use the impact motor of the drilling machine for loosening the drill steel. A further object is to transform the impacts of said impact motor to pulling pulses acting on the drill steel. These objects and others are achieved by providing an attachment according to the present invention, as claimed.